1. Field of the Invention
The present invention relates generally to the field of packaging and more particularly to a new and improved air permeable container cap lining material suitable for use with conventional induction heating/cap sealing techniques.
2. Description of the Prior Art
Prior to the present invention, it has been common practice to line container screw-caps with a laminated material consisting of a layer of pulp to which is wax mounted a layer of aluminum foil. A layer of polyester film is fixed by an adhesive to the foil and film of sealing material is fixed by an adhesive to the polyester layer. The laminate is produced in strips which are ultimately die-cut into discs and mounted in the container cap with a hot melt adhesive. The lined caps are torqued on to a bottle or jar filled with a given product and passed through a high frequency induction heating unit. The aluminum foil is heated to a temperature in the range of about 150-300 degrees Farenheit resulting in melting of the laminating wax between the pulp and foil. The sealing material is selected to match the material used in the bottle or jar and is heat welded or sealed to the rim of the bottle. As the user of the product removes the cap, the pulp will lift with the cap leaving the foil and facing structure on the bottle to provide tamper protection and prevent leakage.
Many products, particularly foods and pharmaceutical products, are packed in a warm condition and contract upon cooling to ambient temperatures, such as coffee creamer. Other products, such as marshmallow creame, are volume-sensitive to changes in ambient air pressure. Since the above described prior art seal is air tight, upon contraction of the product due to cooling or pressure change a plastic container tends to collapse inwardly producing an undesirable appearance which adversely affects the marketability of the product. Conversely, upon product expansion the internal pressure within the container can cause the container to break or the seal to rupture.
One attempted solution to this problem has been to use a finely perforated glassine seal which is secured to the mouth of a bottle or jar using a water base adhesive. The application of the water base adhesive to the bottle or jar is much slower and cumbersome than the heat sealing technique and with hygroscopic products such as instant coffee may lead to contamination of the contents.